The invention relates to a cell module for a battery of a motor vehicle, and also to a method for producing such a cell module.
It is known from the general prior art and, in particular, from the mass production of vehicles, to equip motor vehicles, such as, for example, automobiles with electrified drive trains. Such an electrified drive train is also referred to as an alternative drive train or an alternative drive and includes at least one electric machine that may be operated as an electric motor so as to drive the respective motor vehicle. Consequently, the motor vehicle may be driven in a purely electric manner. Alternatively or in addition, it is contemplated that such a drive train includes an internal combustion engine for driving the motor vehicle, wherein the electric machine may assist, for example, the internal combustion engine when the motor vehicle is being driven. The motor vehicle is consequently configured by way of example as an electric vehicle or a hybrid vehicle.
In order to be able to operate the electric machine in its motor operation, it is necessary to supply the electric machine with electrical current or electrical energy. For this purpose, usually at least one electrical energy storage device in the form of a battery is used, by means of which electrical energy may be stored. The electric machine may be supplied in its motor operation with electrical energy that is stored in the electrical energy storage device. Usually, such an electrified drive train is heavy and expensive.
The object of the present invention is therefore to provide a cell module and also a method for producing such a cell module with the result that the weight and the costs of electrified drive trains for motor vehicles may be kept particularly low.
This and other objects are achieved by a cell module and by a method of producing the cell module in accordance with embodiments of the invention.
A first aspect of the invention relates to a cell module for a battery of a motor vehicle, in particular a motor vehicle such as a passenger car. The cell module comprises a plurality of battery cells for storing electrical energy or electrical current. The cell module may consequently be used in an electrified drive train that comprises by way of example at least one electric machine in its fully produced state. The electric machine may be operated by way of example in a motor operation and consequently as an electric motor, by means of which the motor vehicle may be driven. In order to operate the electric machine in the motor operation, the electric machine is supplied with electrical energy that is stored in the battery and consequently in the cell module or in the battery cells.
Moreover, the cell module comprises a module frame that comprises at least two pressure elements and at least one tension rod that is placed under tension and is formed from a material. The battery cells are arranged between the pressure elements herein. The pressure elements are arranged by way of example spaced from one another along a direction, wherein the battery cells are arranged by way of example along said direction consecutively or one behind the other and between the pressure elements. The pressure elements are clamped against one another by the tension rod whilst arranging the battery cells, as a result of which the battery cells are pressed together. By way of example, the pressure elements are connected to one another via the tension rod that is placed under tension with the result that the battery cells that are arranged between the pressure elements are pressed together. The battery cells are clamped or pushed together by means of the pressure elements by virtue of the fact that the tension rod is placed under tension.
In order to then be able to keep the weight and costs of the cell module and consequently of the battery and also of the electrified drive train overall particularly low, the pressure plates are stressed against one another by way of the tension rod such that a yield strength or the 0.2% yield limit of the material of the tension rod is achieved. In other words, the tension rod is placed under tension so as to brace the pressure elements against one another and consequently to clamp together the battery cells such that the yield strength or the 0.2% yield limit of the material of the tension rod is achieved. The installation space that is required by the cell module and consequently the battery overall may be kept small by using the module frame. Moreover, it is possible to hold the individual battery cells together in a compact manner with the result that the cell module may be handled as a unit that is pre-assembled or may be pre-assembled. As a consequence, the battery may be produced in a particularly simple and consequently rapid and cost-effective manner. The result is that the costs of the battery and consequently of the electrified drive train may be kept low.
Furthermore, owing to the described tensioning of the battery cells that is caused by means of the tension rod, it is possible overall to use particularly cost-effective and lightweight materials for the tension rod and in particular for the module frame. The result is that the weight and the costs of the cell module and consequently of the electrified drive train may be kept particularly low.
The material of the tension rod is by way of example a metal material, in particular a light metal or a light metal alloy such as by way of example aluminum or an aluminum alloy. The result is that the battery cells are clamped together particularly well, and the weight and the costs may be kept particularly low.
The invention is based in particular on the concept of utilizing or selecting elastic characteristics of the material in such a manner that, by way of example, during the serviceable life of the cell module cyclical loads that occur are cushioned, absorbed or compensated in a purely tensile elastic manner, in other words purely by way of tensile elastic characteristics of the material, whereas an increase in length of the cell module that is caused by aging is expediently absorbed by the plastic deformation of the tension rod.
It is preferred that the pressure plates are stressed against one another by the tension rod such that the yield strength or the 0.2% yield limit of the material of the tension rod is precisely achieved, in other words that the tension rod or the material thereof is loaded precisely up to the yield strength or up to the 0.2% yield limit. If, by way of example, an expansion of the battery cells occurs during the serviceable life of the cell module, in particular along the above-mentioned direction along which the pressure elements are spaced from one another, the tension rod thus increasingly extends. Since the yield strength or the 0.2% yield limit has already been achieved, in particular exactly or precisely, prior to the start of the serviceable life of the cell module, each further incremental extension of the tension rod leads to a plastic deformation of the tension rod, wherein this plastic deformation may not or should not lead to a necking in the material of the tension rod until the end of the serviceable life. As a consequence, it is ensured that a tensioning force that is caused by the tension rod for clamping the battery cells together remains at least approximately constant during the serviceable life. In other words, an at least approximately uniform load on the battery cells may be ensured over the serviceable life. Consequently, varying mechanical loads on the battery cells may be avoided over the serviceable life. Moreover, the material or material characteristics of the tension rod may be at least approximately entirely utilized with the result that it may be overall possible to avoid overdimensioning the tension rod and, consequently, the module frame, which would be disadvantageous with regards to weight and cost. The weight and the costs may consequently be kept low.
The yield strength is usually referred to as Re and is a material characteristic value and refers to the tension value up to which the material does not show any permanent plastic deformation in the case of a uniaxial and torque-free tensile load. In this case, it is a yield point. The battery cells that are arranged between the pressure elements and, by way of example are arranged one behind the other or consecutively, form a battery pack, the length of which may increase by way of example as a result of aging. As a consequence, this increase in length increases—starting from the yield strength or from the 0.2% yield limit—the load that is acting upon the tension rod or the extension of the tension rod with the result that the tension rod deforms in a plastic manner.
In an advantageous embodiment, the yield strength is the upper yield strength that is usually also referred to as ReH. If the material of the tension rod comprises, by way of example, an upper yield strength ReH and also a lower yield strength ReL, then the above-mentioned yield strength is preferably the upper yield strength ReH. The result is that an increase in length of the battery pack and consequently an increasing extension of the tension rod—starting from the upper yield strength—leads to a plastic deformation of the tension rod.
It has proven particularly advantageous if one of the pressure elements is provided as a fixed bearing that may be fixed to a component, in particular a housing, of the battery. The battery consequently comprises in its fully produced state the cell module and at least one further component that is configured by way of example as a housing. The cell module herein is held on the further component. It is preferably provided herein that one of the pressure elements is configured as a fixed bearing that is fixed or may be fixed on the further component, in particular the housing, of the battery. As a consequence, a defined and secure and also light and cost-effective holding arrangement of the cell module may be ensured without an excessive number of additional heavy and cost-intensive holding elements being provided and being required.
In order to keep the costs and the weight of the cell module particularly low, it is provided in the case of a further embodiment of the invention that the other pressure element is configured as a floating bearing that permits the other pressure element to be displaced relative to the component of the battery. In other words, the other pressure element is preferably a floating bearing and is consequently expediently configured in such a manner that it may be displaced. As a consequence, tensions and consequently excessive loads on the cell module may be avoided. The result is that the cell module may be provided in a particularly light and cost-effective manner.
In a further embodiment of the invention, the yield strength or the 0.2% yield limit is achieved in the fully charged state of the battery cells. As a consequence, in particular at the start of the serviceable life of the cell module, a defined state is achieved and starting from said defined state, if the length of the battery pack is increased, a desired plastic deformation of the tension rod occurs. In particular, it is possible by way of this embodiment to cushion, to absorb or to compensate cyclical loads in a purely tensile elastic manner. If by way of example starting from the fully charged state of the battery cells a reduction in length or a decrease in length of the battery pack occurs, whereupon an increase in length of the battery pack occurs again in such a manner that the yield strength or the 0.2% yield limit is not exceeded, these length changes may thus be absorbed in an elastic, in particular tensile elastic, manner, in other words by means of the elastic deformation of the tension rod. However, if the length increases as a result of aging starting from the yield strength or the 0.2% yield limit, the yield strength or 0.2% yield limit is exceeded. The result is that increases in length of this type are absorbed by plastic deformation of the tension rod.
In order to keep the weight and the costs of the cell module particularly low, it is provided in a further embodiment of the invention that the tension rod is connected to the pressure elements in a materially-bonded manner. For this purpose, the tension rod is by way of example welded to the pressure elements. By way of example, the pressure elements are formed from a metal material. Moreover, it is contemplated for the pressure elements to be configured as pressure plates.
A battery for a motor vehicle, in particular a car such as a passenger car, is also associated with the invention, wherein the battery comprises at least one cell module in accordance with the invention. Advantages and advantageous embodiments of the cell module in accordance with the invention are to be viewed as advantages and advantageous embodiments of the battery in accordance with the invention, and vice versa.
A second aspect of the invention relates to a method for producing a cell module for a battery of a motor vehicle, in particular a cell module in accordance with the first aspect of the invention. In a first step of the method, a plurality of battery cells is provided for storing electrical energy or electrical current. In a second step of the method, a module frame is provided that comprises at least two pressure elements and at least one tension rod that is formed from a material, in particular a metal material. In a third step of the method, the battery cells are arranged between the pressure elements. By way of example, the pressure elements are arranged in such a manner that they are spaced from one another along a direction. The battery cells herein are arranged by way of example between the pressure elements in such a manner that the battery cells are arranged along said direction one behind the other or consecutively. In a fourth step of the method, the pressure elements are stressed against one another by the tension rod whilst arranging the battery cells, as a result of which the tension rod is placed under tension. The pressure plates herein are stressed against one another by means of the tension rod in such a manner that the material of the tension rod achieves a yield strength or the 0.2% yield limit, in particular precisely or exactly. Advantages and advantageous embodiments of the first aspect of the invention are to be viewed as advantages and advantageous embodiments of the second aspect of the invention, and vice versa.
It is preferred that the yield strength or the 0.2% yield limit of the material of the tension rod is achieved exactly directly after the production of the cell module and consequently at the start of its serviceable life. As a consequence, cyclical loads—in particular starting from the yield strength or 0.2% yield limit—may be absorbed by means of elastic deformation of the tension rod, wherein increases in length that are caused by aging are absorbed by the plastic deformation of the tension rod. This means by way of example that at the start of the serviceable life of the cell module, the module frame is preferably loaded with fully-charged battery cells precisely up to the yield strength, in particular ReH, or up to the 0.2% yield limit (Rp,0.2). Each further incremental extension of the tension rod leads to a plastic deformation of the tension rod, as a result of which it is ensured that a tensioning force for clamping the battery cells together that acts upon the battery cells and is caused by the module frame remains at least at an approximately constant level.
In the case of an advantageous embodiment of the second aspect of the invention, it is provided that the battery cells are clamped against one another by a compression device that differs from the module frame. In the state in which said battery cells are pressed together by the compression device, said battery cells are provided with the module frame. In particular, by way of example it is initially provided that the pressure elements and the battery cells that are arranged between the pressure elements are pressed together by the compression device with the result that the battery cells that are arranged between the pressure elements are pressed together via the pressure elements by the compression device and consequently said battery cells are pushed together or pressed together. In this state, the tension rod is coupled to, in particular connected to, the pressure elements, whereupon by way of example the cell module is released from the compression device or whereupon the compression that is effected by the compression device is terminated. The material of the tension rod herein achieves the yield strength or the 0.2% yield limit, in particular precisely or exactly, preferably directly or immediately after the compression that is effected by the compression device is terminated. As a consequence, at the start of the serviceable life of the cell module, a defined starting state is achieved and, starting from said defined state, cyclical loads may be absorbed by means of elastic deformation. However, increases in length of the battery pack that are caused by aging may be absorbed by means of plastic deformation of the tension rod. As a consequence, particularly light and cost-effective materials may be used for the tension rod.
Finally, it has proven particularly advantageous if the tension rod is connected to the pressure elements in the state in which the battery cell is pressed together by the compression device. As a consequence, by way of example the tension rod is then and only then placed under tension if the compression that is effected by the compression device is terminated, in other words if the compression device is released from the cell module. The tension rod is consequently used in order to contribute to or to cause a compression of the battery cells after the compression of the battery cells that is caused by the compression device is terminated. The result is that the tension rod is placed under tension. A defined state and, in particular, a defined starting state and also a defined load on the tension rod, in particular at the start of the serviceable life of the cell module, may be realized by means of this connection of the tension rod to the pressure elements. It is consequently possible in a defined manner by means of elastic deformation of the tension rod to compensate cyclical loads or changes in length and by means of plastic deformation of the tension rod to absorb increases in length of the battery pack that are caused by aging. Consequently, the costs and the weight of the cell module may be kept particularly low.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
In the figures, identical or functionally identical elements are provided with identical reference numerals.